Polymer materials for geomembranes are selected for chemical resistance, mechanical properties (elastic modulus, yield strength, puncture/tear resistance), weathering resistance, product life expectancy, installation factors and cost effectiveness. The properties of polymeric geomembranes are effected by polymer structure, molecular weight and crystallinity. The degree of crystallinity effects the performance properties of the geomembrane, including the mechanical properties and chemical resistance.
Medium density polyethylene (“MDPE”) and high density polyethylene (“HDPE”) have been used in polyolefin-based geomembrane applications. It is believed that the crystalline nature of these polymers is responsible for density, stiffness, permeability, and chemical resistance. As compared to other polymers, MDPE and HDPE are low cost polymers and have good physical property balances, chemical resistance, and ultraviolet weathering performance. Also, MDPE and HDPE are easily processed in blown and flat die extrusion processes.
Unfortunately, geomembranes made with MDPE or HDPE tend to lack flexibility and impact resistance. Those characteristics can be more pronounced in cold climate or cold environment applications. For some geomembrane applications, it is useful to provide improved polyolefin-based compositions made with or containing MDPE or HDPE, having flexibility, impact resistance, dimensional stability, environmental stress cracking resistance (ESCR), and temperature resistance.